1. Field
The present disclosure relates an engine torque estimator for an internal combustion engine and a method of estimating an engine torque for the internal combustion engine.
2. Description of the Related Art
One known example of an engine torque estimator for an internal combustion engine is disclosed in Japanese Unexamined Patent Application Publication No. 11-50889. The engine torque estimator calculates a target shaft torque, friction loss torque, indicated torque, and pump loss torque on the basis of running states of the engine (e.g., the amount of operation of an accelerator, rotational speed, water temperature, amount of air) and then estimates an engine torque by computation using them. Specifically, the indicated torque is calculated by adding the friction loss torque and target shaft torque, and the pump loss torque is calculated by searching a predetermined map on the basis of an intake pressure. The engine torque is calculated on the basis of the calculated indicated torque and pump loss torque.
Typically, a combustion state in the engine varies every moment. Thus, it is presumed that the temperature inside a cylinder and the cylinder internal pressure vary and, with that variation, the indicated torque and pump loss torque also vary. Accordingly, during transient driving in which variations in the combustion state are significantly large, it is difficult to properly assess the pump loss torque, and it is therefore difficult to properly estimate the engine torque during the transient driving.
One example of a device for calculating a pump loss torque in controlling the torque of the engine is disclosed in Japanese Unexamined Patent Application Publication No. 2006-291803. The device disclosed in that patent document calculates the pump loss torque by searching a predetermined map on the basis of an intake pressure difference (=atmospheric pressure−intake manifold pressure) and an engine rotational speed. In a combustion stop period for which fuel is cut off, the degree of accuracy in calculation of the pump loss torque is enhanced by correcting the pump loss torque in accordance with the atmospheric pressure, estimated indicated torque, intake manifold pressure, engine rotational speed, and engine water temperature.